1. Field of the Invention
The present invention relates to a method for interpolating adjacent flames by at least one interpolation frame to shorten a display flame interval in reproducing a video. In a hold type image display unit which continues displaying a previous flame until a new image is written, for example, a liquid crystal display and an electro luminescence display, a blurring phenomenon by which the eyes of a viewer follow movement of a moving object or an unnatural movement due to display of an moving image of a few frames is a problem in displaying the moving image.
2. Description of the Related Art
This problem can be solved by shortening a display frame distance. As a method for realizing shortening the display frame distance, there is a method of generating an interpolation frame using motion compensation used in MPEG2 (Motion Picture Experts Group phase 2) and interposing the interpolation frame between the frames adjacent thereto. In the motion compensation in MPEG2, a motion vector detected by block matching method is used. The block matching method is a method including dividing a first reference frame into a plurality of first blocks, searching a second reference frame adjacent to the first reference frame for a second block having a maximum correlation with respect to each of the first blocks, and computing a motion vector from the second block to the first block.
In a frame interpolation method using such a motion compensation, when an interpolation frame is generated by the motion compensation, at first the motion vector between the first reference frame and the second reference frame is scaled to a second motion vector between the interpolation frame and the first reference frame. An interpolation frame is generated by carrying out the motion compensation by means of the second motion vector obtained by scaling. In other words, the end of the second motion vector is fixed on the first reference frame.
Image data of the block of the first reference frame that is indicated by the end of the second motion vector is copied to the block on the interpolation frame that is indicated by the starting point of the second motion vector.
In this method, the starting point position of the second motion vector provided by scaling does not always coincide with the position of an to-be-interpolated block on the interpolation frame. As a result, a clearance having no image data or a region on which images are superposed is formed on the interpolation frame.
Japanese patent No. 2528103 discloses a frame interpolation method without clearance between images or superposition of the image. In this prior method, the frame interpolation is carried out by computing a correlation between forward and backward reference frames that are geometrically symmetrical with respect to the to-be-interpolated block on the interpolation frame. As a result, an interpolation frame can be generated directly by a motion vector obtained first without scaling a motion vector. In addition, since the to-be-interpolated blocks on an interpolation are considered as blocks of the same lattice, the interpolation frame does not occur a clearance between images and superposition of images.
On the other hand, Japanese Patent Laid-Open No. 2001-24988 discloses a method for a motion compensation by computing a reliability of a motion compensation on the basis of a differential value between images in estimating a motion and a size of detected motion vector, and performing a compensation by another method when the reliability is low. Since the method of patent document 1 determine a motion vector only from a correlation between frames forward and backward the interpolation frame, the motion vector that reflects an actual movement is not always provided. For this reason, the quality of the interpolation frame deteriorates, resulting in deteriorating quality of the whole video.
On the other hand, the method of a patent document 2 may theoretically dissolve the problem of the deterioration of the interpolation frame due to erroneous detection of the motion vector in the patent document 1. However, it is difficult for it to be realistic to measure reliability of motion compensation only by a differential value between images in estimating a movement or a size of a motion vector. Therefore, it cannot generate always an appropriate interpolation frame.
It is an object of the present invention to provide an interpolation image generating method for generating an interpolation image with high quality, and an apparatus therefor.